I. Field of the Invention
This invention relates to a process for the denitrogenation of nitrogen-containing hydrocarbon compounds, or feedstocks containing nitrogen-containing hydrocarbon compounds, via a low hydrogen intensive mechanism. In particular, it relates to a process for the selective denitrogenation of nitrogen-containing hydrocarbons, especially one for the selective cleavage, in the presence of hydrogen, of an aryl carbon-nitrogen bond from an aryl nitrogen-containing hydrocarbon without prior saturation with hydrogen of a non-nitrogen containing aryl moiety which constitutes a portion of said aryl nitrogen-containing hydrocarbon; especially a non-nitrogen containing aryl moiety directly attached to the nitrogen being removed.
II. Background
The denitrogenation of nitrogen-containing hydrocarbon feedstocks, or removal of nitrogen from nitrogen compounds, requires hydrogenation of the nitrogen compounds. The reaction proceeds rapidly with lower boiling feedstocks, but becomes much slower as the boiling range of the feedstock increases. With high boiling range feedstocks, e.g., heavy vacuum gas oils and residua, denitrogenation becomes more difficult, and complete denitrogenation is not obtained even in high severity reactions with the best of presently commercially available catalysts. Hydrodenitrogenation processes require greater consumption of hydrogen as the severity of the process conditions is increased.
There are several reasons which make the hydrodenitrogenation of hydrocarbon feedstocks difficult. For one thing, side reactions occur which often form product nitrogen compounds which are more difficult to denitrogenate than the original nitrogen-containing reactant. Additional hydrogen must then be consumed to achieve a satisfactory level of hydrodenitrogenation. Moreover, the amount of nitrogen in a feedstock increases markedly with increased boiling range. If the rate constant for denitrogenation remained the same, it might be expected that the greater quantities of nitrogen present would not affect the rate of denitrogenation. This, however, is not the case. Apparently the increased size of the non-nitrogen portion of the molecule reduces the rate constant for denitrogenation, perhaps by making contact between the nitrogen-containing compounds and the active sites of the catalyst more difficult.
Processes using conventional catalysts thus require the consumption of excessive amounts of hydrogen, far more hydrogen than required for stoichiometric hydrodenitrogenation of the nitrogen-containing aromatic components of the feed. This is because such reactions generally occur through a network of reaction paths, and the predominant hydrodenitrogenation reaction path in such reactions, if satisfactory levels of nitrogen-removal are to be attained, requires prior hydrogenation of the non-nitrogen containing arene, aryl, or aromatic ring, or rings, particularly those adjacent to, and adjoined via a nuclear or ring carbon atom with the nitrogen atom of the nitrogen-containing heterocyclic ring to be denitrogenated. Moreover, at conditions required for satisfactory nitrogen removal, other non-nitrogen containing aromatic molecules can also be saturated; this further increasing hydrogen consumption. This results in a substantial increase in hydrogen consumption over that which is necessary for stoichiometric nitrogen removal. Conventional hydrodenitrogenation processes are thus plagued by the requirement for excessive hydrogenation prior to the achievement of satisfactory denitrogenation.
In conventional hydrodenitrogenation reactions, as when the hydrodenitrogenation reactions are conducted with conventional nickel-molybdenum or cobalt-molybdenum catalysts, to effect a high level of nitrogen removal extensive hydrogenation is required. Consider, e.g., the following reactions which have been found to occur in the hydrodenitrogenation of model compounds, i.e., (1) the hydrodenitrogenation of aromatic amines or aromatic polyamines, e.g., aniline; (2) the hydrodenitrogenation of C.sub.4 N type heterocyclic nitrogen-containing compounds such as pyrrole, indole, or carbazole type compounds, which include an aromatic ring substitutent, or substitutents; (3) the hydrodenitrogenation of heterocyclic aromatic compounds of the C.sub.5 N type, such as pyridine, quinoline, or acridine type compounds, which include an aromatic ring substitutent, or substitutents; and (4) the hydrodenitrogenation of carbazole type compounds, e.g., carbazole, to wit: ##STR1##
In the hydrodenitrogenation of analine (1A), supra, the aromatic ring is first saturated, and the amino group is then cleaved from the aromatic ring. Cyclohexane (1B) and ammonia are produced, four moles of hydrogen being required; three moles to saturate the aromatic ring and another mole of hydrogen to remove the nitrogen from the ring and form ammonia. In accordance with the series of reactions (2), six moles of hydrogen are required to remove the nitrogen from the ring as ammonia. In the sequence of reactions (3), seven moles of hydrogen are required to remove the nitrogen from the ring. In each set of reactions (2) and (3) the ring containing the nitrogen is first saturated with hydrogen, and thereafter the carbon-nitrogen bond is broken to form the aniline derivative, o-ethylaniline (2C) and o-propylaniline (3C), respectively. Before the second carbon-nitrogen bond is broken, however, the aromatic ring is then saturated to form 1-amino-2-ethylcyclohexane (2D) and 2-propylcycohexylamine (3D), respectively. Thereafter the carbon-nitrogen bonds of these compounds are broken to form ethylcyclohexane (2E) and propylcyclohexane (3E), respectively. In the sequence of reactions (4), eight moles of hydrogen are required to remove the nitrogen from the ring. First, one of the aryl rings is saturated with hydrogen (4A, 4B). Thereafter, the first carbon-nitrogen bond is broken (4C). Next, the last aryl ring is saturated with hydrogen (4D) and thereafter the second carbon-nitrogen bond is broken and nitrogen is then removed from the ring (4D, 4E). Mechanistically, the difficulty associated with all of these reactions is that the aromatic rings must be saturated with hydrogen prior to the final cleavage of the carbon-nitrogen bond which separates the nitrogen atom from the molecule. Thus, at normal denitrogenation conditions hydrogen is used up in producing saturation of aromatic rings which contribute nothing towards denitrogenation, or the removal of nitrogen from nitrogen-containing compounds. Saturation of the non-nitrogen containing aromatic rings does little, if anything, to improve the quality of the product; or, in any event, this is clearly wasteful of hydrogen, and may in some actually decrease the value of the product. Thus, there is a very serious need to provide a novel process which utilizes a less hydrogen intensive mechanism to produce cleavage of carbon-nitrogen bonds.
III. Objects
It is, accordingly, an objective of the present invention to fulfill this need; especially by providing a novel process for the denitrogenation of a nitrogen-containing compound, or compounds, via a non-hydrogen intensive mechanism.
It is, in particular, an object of this invention to provide a novel process for the denitrogenation of nitrogen-containing hydrocarbon feeds, particularly one which effectively denitrogenates such feeds at relatively low temperature and low hydrogen partial pressures.
A more specific object is to provide a process for the selective removal of nitrogen from nitrogen-containing hydrocarbons, or nitrogen-containing hydrocarbon feed components, via a catalytic reaction which removes at relatively low temperatures and low hydrogen partial pressures major amounts of the nitrogen from the nitrogen-containing hydrocarbon, or nitrogen-containing hydrocarbon feed components, by cleavage of carbon-nitrogen bonds, with reaction between the cleaved nitrogen moiety and hydrogen without excessive saturation with hydrogen of the nitrogen-containing hydrocarbon, or nitrogen-containing hydrocarbon feed components, from which the nitrogen has been cleaved.
A yet more specific object is to provide a process for the selective cleavage of an aryl carbon-nitrogen bond of an aryl nitrogen-containing hydrocarbon, or hydrocarbons, or feed containing such hydrocarbon, or hydrocarbons, at relatively low temperatures and low hydrogen partial pressures, without the prior saturation with hydrogen of a non-nitrogen containing aryl moiety constituting a portion of said aryl nitrogen-containing hydrocarbon, or hydrocarbons; especially a non-nitrogen containing aryl moiety directly attached to the nitrogen being removed.
IV. The Invention
These objects and others are achieved in accordance with the present invention embodying a process wherein a feed comprising a nitrogen-containing hydrocarbon compound, or compound containing a carbon-nitrogen bond, is contacted in the presence of hydrogen over a catalyst which contains elemental iron and one or more of an alkali or alkaline-earth metal [i.e., a Group IA or IIA metal (Periodic Table of the Elements, E. H. Sargent & Co., Copyright 1964 Dyna-Slide Co.)], or compound thereof, and preferably additionally a Group IIIA metal, or metal compound, particularly aluminum, or compound thereof, sufficient to selectively cleave said carbon-nitrogen bond and denitrogenate said nitrogen-containing hydrocarbon compound at low temperatures, or temperatures ranging no higher than about 430.degree. C. The process attains its highest usefulness in selectively cleaving the aryl carbon-nitrogen bond of a nitrogenous hydrocarbon compound, or compounds, containing said aryl carbon-nitrogen bond. In a compound, or compounds, characterized by the presence of a nitrogen atom bound via a single bond to a nuclear, or ring carbon atom of an arene, aryl or aromatic ring, cleavage of the carbon-nitrogen bond is produced without significant hydrogen saturation of said arene, aryl or aromatic ring. In the preferred aspects of practicing this invention, a feed comprised of a hydrocarbon compound, or compounds, containing a carbon-nitrogen bond is contacted, with hydrogen, over an alkali or alkaline-earth metal promoted iron catalyst at temperature ranging from about 225.degree. C. to about 430.degree. C., preferably from about 250.degree. C. to about 400.degree. C., more preferably from about 300.degree. C. to about 370.degree. C., and at hydrogen partial pressures ranging from about 0 pounds per square inch gauge (psig) to about 1000 psig, preferably from about 0 psig to about 600 psig, and more preferably from about 0 psig to about 400 psig, sufficient to cleave said carbon-nitrogen bond and denitrogenated said nitrogen-containing hydrocarbon compound, or compounds. In particular, it relates to such process wherein the feed is comprised of an admixture of hydrocarbon compounds, inclusive of one or more of said nitrogen-containing hydrocarbon compounds. More particularly, it relates to such process wherein a feed comprising a hydrocarbon compound, or compounds, the molecule of which is characterized by the presence of a nitrogen atom bound via a single bond to a nuclear, or ring carbon atom of an arene, aryl, or aromatic ring, is contacted in an atmosphere of low pressure hydrogen over said iron catalyst sufficient to cleave said carbon-nitrogen bond without significant hydrogen saturation of the arene, aryl, or aromatic ring attached to said nitrogen being removed.
The alkali or alkaline-earth metal promoted iron catalyst required for use in this invention can be supported or unsupported, but in either instance it is one the catalytic surface of which is constituted essentially of metallic, or elemental iron (Fe.degree.) crystallites about which the alkali or alkaline-earth metals are dispersed, generally as a monolayer of an alkaline oxide or alkaline-earth metal oxide. The elemental iron catalyst containing the alkali or alkaline-earth metal, or compound thereof, is capable of high conversion of aniline (activity), at high selectivity to benzene. For example, a moderately active catalyst, as used pursuant to this invention, is sufficient at 300.degree. C. and 0 psig to convert pure aniline, added with hydrogen in a molar ratio of hydrogen:aniline of 3:1, at a liquid hourly space velocity (LHSV) of 1, at a conversion level of 50 mole percent, or greater, to a liquid product containing 99 mole percent, or greater, benzene. Such combination of high activity, and selectivity, at this low temperature and pressure does not occur with conventional hydrodenitrogenation catalysts. The catalysts employed in conventional hydrodenitrogenation processes are sulfided, and produce hydrodenitrogenation reactions characterized very closely by the network reaction sequence (1), (2), (3), and (4), supra. The catalyst employed in the process of this invention on the other hand is unsulfided, and can function in the presence of sulfur only when a sufficient portion of the catalytic surface of the catalyst is substantially metallic, or elemental iron (Fe.degree.). The formation of sufficiently high concentrations of sulfur at the catalyst surface tends to produce catalyst deactivation via the formation of iron sulfide upon the catalyst surface. Commercial hydrodenitrogenation catalysts are sulfided species, and require high temperature to obtain conversion of a typical hydrocarbon feed, and the selectivity of such catalysts is very low. In the practice of this invention, sulfur or sulfur compounds in concentrations greater than about 5000 ppm, preferably greater than about 2000 ppm, and more preferably greater than about 500 ppm calculated as elemental sulfur based on the weight of the feed, should preferably be avoided. Sulfur introduced into the feed in concentrations greater than these more rapidly deactivate the catalyst by converting a major portion of the metallic, or elemental iron surface of the catalyst to iron sulfide.
In a preferred embodiment of the invention, an arene, aryl, or aromatic heterocyclic nitrogen hydrocarbon, or hydrocarbons, containing at least one aryl carbon-nitrogen bond, or feedstock containing such hydrocarbon, or hydrocarbons, is contacted with hydrogen, over said iron catalyst, preferably over a fused iron catalyst, at reaction conditions sufficient to cleave the aryl carbon-nitrogen bond, or bonds, before significant hydrogenation, and preferably without hydrogenation of the aromatic ring portion of the molecule; particularly the aromatic ring bonded via a ring carbon atom to the nitrogen being removed. Suitably, the aryl carbon-nitrogen bond, or bonds, are cleaved, and the cleavage site, or sites, healed with hydrogen, without saturation of the aromatic ring portion of the molecule by conducting the reaction at temperatures ranging from about 225.degree. C. to about 430.degree. C., preferably from about 250.degree. C. to about 400.degree. C., more preferably from about 300.degree. C. to about 370.degree. C., and under an atmosphere of hydrogen gas or admixture of hydrogen and another gas, or gases within which the hydrogen partial pressure ranges from about 0 psig to about 1000 psig, preferably from about 0 psig to about 600 psig, and more preferably from about 0 psig to about 400 psig. Some positive pressure of hydrogen is necessary in conducting the reaction, though the hydrogen pressure can thus be at atmospheric pressure, or less. The combination of temperature and hydrogen partial pressure are preferably such that a part of the feed, at reaction conditions, is in vapor phase. Temperatures above about 430.degree. C. generally cause cracking of the feed, which can lower liquid yields. At temperatures below about 225.degree. C., on the other hand, the rate of reaction is generally too slow to be practical. Total pressures are not critical, but generally range from about 0 psig to about 2000 psig, preferably from about 0 psig to about 1200 psig. Space velocities range from about 0.01 LHSV to about 20 LHSV, preferably from about 0.1 LHSV to about 5 LHSV.
The present process is useful for the removal of nitrogen from a nitrogen-containing hydrocarbon compound, or compounds. Its highest utility, however, is based on the discovery that nitrogen can be selectively removed, at high levels, from a molecule characterized by the presence of a nitrogen atom bound via a single bond to a nuclear, or ring carbon atom of an aryl group or aromatic ring, with minimal hydrogen saturation, if any, of said aryl group or aromatic ring containing the carbon atom to which the nitrogen is bonded. The mechanism of conventional hydrodenitrogenation requires significant saturation with hydrogen of the unsaturated bonds of the aryl group or aromatic ring portion of the molecule to which the targeted nitrogen atom is bound prior to nitrogen cleavage and separation of nitrogen from the molecule. Unlike conventional hydrodenitrogenation, the present process produces cleavage of the carbon-nitrogen bond, separation of the nitrogen from the molecule, healing with hydrogen of the carbon site from which the nitrogen was broken, and hydrogenation of the nitrogen with minimal hydrogen saturation, if any, of said aryl group or aromatic ring portion of the molecule to which said targeted nitrogen atom is bound. This invention is highly selective, and in its preferred aspects can be further characterized as one wherein at least about 50 weight percent, preferably at least about 75 weight percent, and more preferably from about 90 weight percent to about 100 weight percent, of the nitrogen removed from the parent aromatic nitrogen-containing hydrocarbon compound, or compounds, is the result of denitrogenation via cleavage of said aryl carbon-nitrogen bond, or bonds, with separation of the nitrogen from the molecule and healing with hydrogen of the carbon site of said original feed compound, or compounds, from which the nitrogen was broken, or cleaved, without hydrogen saturation of said aryl or aromatic rings bonded via a nuclear or ring carbon atom to the nitrogen removed from said nitrogen-containing aromatic hydrocarbon compound, or compounds, of the original feed. The selectivity of the process of this invention is sharply contrasted with conventional processes. In the more conventional hydrodenitrogenation reactions, as when the hydrodenitrogenation reactions are conducted to denitrogenate nitrogen-containing aromatic hydrocarbons over conventional nickel-molybdenum or cobalt-molybdenum catalysts, excessive hydrogenation of the aryl or aromatic rings, a nuclear or ring carbon atom of which forms an aryl carbon-nitrogen bond, occurs prior to the cleavage and removal of nitrogen from the molecule.
Whereas there is no desire to be bound by any specific theory of mechanism, it is believed that in hydrodenitrogenating a nitrogen-containing hydrocarbon compound which contains an aryl carbon-nitrogen bond either the iron catalyst, at the conditions of operation, activates the aryl carbon-nitrogen bond sufficiently that it cleaves before hydrogenation of the ring can occur, or the catalyst complexes or ties up the attached aryl or aromatic ring such that hydrogenation of the ring does not compete favorably with aryl carbon-nitrogen bond hydrogenolysis.
The following series of reactions (5), (6), (7), (8) are representative of the low hydrogen intensity reactions which occur in the process of this invention. Reference is also made to reactions (1), (2), (3), (4) to which these reactions can be compared. ##STR2##
In the hydrodenitrogenation of aniline (5A), the amino group is hydrogenated and cleaved from the aromatic ring, ammonia and benzene (5B) being produced in substantially stoichiometric quantities without saturation of the aromatic ring. Thus, only one mole of hydrogen is required to effect cleavage and removal of nitrogen from the ring whereas, in contrast, four moles of hydrogen are required to form cyclohexane and ammonia in (1), supra.
Indole (2A, 6A) reacts with one mole of hydrogen to form 2,3-dihydroindole (2B, 6B), and quinoline (3A, 7A) reacts with two moles of hydrogen to form 1,2,3,4-tetrahydroquinoline (2B, 6B). After saturation of the nitrogen-containing ring the carbon-nitrogen bond of the 2,3-dihydroindole (2B, 6B) is broken consuming one additional mole of hydrogen to form o-ethylaniline (2C, 6C), and the carbon-nitrogen bond of the 1,2,3,4-tetrahydroquinoline is broken consuming one additional mole of hydrogen to form o-propylaniline (3C, 7C). From this point on, however, the sets of reactions represented by reaction sequences (2) and (3) differ radically from those represented by reaction sequences (6) and (7). In either of reactions (2) and (3) the aryl or aromatic ring of the o-ethylaniline (2C, 6C) or the o-propylaniline (3C, 7C) must be saturated with hydrogen before the second carbon-nitrogen bond is cleaved to remove the nitrogen from the ring. Three moles of hydrogen are thus required to saturate the aromatic ring to form 1-amino-2-ethylcyclohexane (2D) and 2-propylcyclohexylamine (3D) from the o-ethylaniline (2C) and o-propylaniline (3C), respectively. An additional mole of hydrogen is then required to form from these ring-saturated compounds ethylcyclohexane (2E) and propylcyclohexane (3E), respectively. In contrast, ethylbenzene (6D) can be formed directly from o-ethylaniline (6C) and propylbenzene (7D) from o-propylaniline (7C) with the consumption of only one additional mole of hydrogen rather than four. In addition 2,3-dihydroindole (6B) can be directly denitrogenated to ethylbenzene (6D) and 1,2,3,4-tetrahydroquinoline (7B) to propylbenzene (7D).
It will be observed, to summarize, that in the reaction sequence described in (2), supra, a total of six moles of hydrogen are required to remove the nitrogen from the aromatic ring, and that in reaction sequence (6) only three moles of hydrogen are required. In reaction sequence (3) seven moles of hydrogen are required to remove the nitrogen from the aromatic ring, and in reaction sequence (7) only four moles of hydrogen are required. Thus, in either of reaction sequences (2 and 3) or (6 and 7) before the catalyst can effectively break a nuclear carbon-nitrogen bond it must first saturate the rings which contain the nitrogen atom. Having broken the carbon-nitrogen bond between the nitrogen and the saturated ring, the conventional catalyst in accordance with (2) and (3), supra, must then proceed to saturate the remaining ring prior to breaking the second carbon-nitrogen bond. Only then can the nitrogen be removed as ammonia. Not so in accordance with the mechanism provided by the iron catalyst in accordance with the process of this invention. Rather, the aryl carbon-nitrogen bond of the o-ethylaniline (2C) or o-propylaniline (6C) is readily broken without saturation of the ring, one mole of hydrogen being required to heal the hydrogen deficient carbon of the broken carbon chain and further hydrogenate the nitrogen.
Carbazole, a very refractory nitrogen-containing compound, can also be hydrodenitrogenated in accordance with this invention with minimal hydrogen consumption. In reaction sequence (8) supra, only two moles of hydrogen are required to cleave the nitrogen from the two aromatic rings, of carbazole (8A), breakout the nitrogen and form biphenyl (8B) and ammonia. No hydrogen is required to saturate either of the aromatic rings prior to cleavage of the carbon-nitrogen bonds; a saving of six moles of hydrogen. In contrast, a total of eight moles of hydrogen are required to remove nitrogen from carbazole (4A) in accordance with reaction sequence (4) by the use of a conventional catalyst. In accordance with reaction sequence (4), carbazole (4A) is first converted to hexahydrocarbazole (4B), this utilizing three moles of hydrogen to saturate the first aromatic ring. An additional mole of hydrogen is required to form 2-cyclohexylaniline (4C) from hexahydrocarbazole (4B), an additional three moles to form 2-cyclohexyl-cyclohexylamine (4D), and yet an additional mole of hydrogen to form bicyclohexyl (4E) and ammonia.
2-Cyclohexylaniline, it is found by the practice of this invention, can be converted directly to cyclohexyl benzene with the consumption of only one mole of hydrogen, and hexahydrocarbazole can be converted directly to cyclohexylbenzene with the consumption of only two moles of hydrogen.
The catalyst is constituted of elemental iron, modified with one or more alkali or alkaline-earth metals, or compounds thereof, sufficient to produce on contact at reaction conditions selective aryl carbon-nitrogen bond cleavage. The selective aryl carbon-nitrogen bond cleavage reaction occurs over catalysts which contain iron, preferably as the major component, or major metal component. The catalyst may be unsupported or supported, i.e., it may be bulk (unsupported) iron, or iron dispersed upon a support. The unsupported, or bulk iron catalyst is preferred and it may be employed as essentially metallic iron in bulk, or unsupported iron which preferably contains alkali or alkaline-earth metals, or the oxides of such metals, exemplary of which are sodium, potassium, cesium, magnesium, calcium, barium, or the like. The active iron catalyst, when a bulk iron catalyst, is preferably one which contains at least 50 percent elemental iron, more preferably from about 70 percent to about 98 percent elemental iron, based on the weight of the catalyst. The iron catalyst, when a catalyst wherein the iron is distributed or dispersed upon a support, contains at least about 0.1 percent iron (measured as elemental iron), preferably from about 0.1 percent to about 50 percent iron, and more preferably from about 5 percent to about 25 percent iron, based on the total weight of the catalyst, and the supported metallic component, exclusive of the support component, or components, contains at least 50 percent iron (measured as elemental iron), and preferably from about 70 percent to about 98 percent iron.
A bulk or unsupported fused iron catalyst is preferred. The fused iron catalyst is one prepared by heating and melting the iron, thus fusing the iron with an alkali or alkaline-earth metal, or metals, or with an alkali or alkaline-earth metal compound, or compounds, which are generally present in concentrations ranging from about 0.01 percent to about 10 percent, preferably from about 0.2 percent to about 4 percent, based on the total weight of catalyst. Sodium, potassium, cesium, magnesium, calcium, and barium are the preferred alkali or alkaline-earth metals. Aluminum is also a preferred component of the fused iron-alkali or alkaline earth metal catalyst, and it can be present as aluminum metal or an aluminum compound, or compounds, especially as an aluminum oxide. The aluminum metal, or compound thereof, is preferably contained in the catalyst in concentration ranging from about 0.01 percent to about 20 percent, preferably from about 0.5 percent to about 5 percent, calculated as aluminum oxide based on the weight of the catalyst. Other metals may also be used as promoters and/or modifiers which are added to and contained within the catalyst, such metals including rhenium, nickel, cobalt, palladium, platinum, and copper. Such metals may be added to the catalyst alone or admixed one metal with another, or with other metals.
The iron-based catalyst, as suggested, may also be supported; preferably upon an inorganic oxide support. Supports include, but are not limited to, the oxides of aluminum, silicon, boron, phosphorous, titanium, zirconium, calcium, magnesium, barium, and mixtures of these and other components. Other supports may include clays, such as bentonite, zeolites and other alumino-silicate materials, e.g., montmorillionite. Additional supports may be selected from the group of refractory carbides and nitrides of the transition metals of Groups IVB, VB, VIB, VIIB, and Group VIII iron group metals. Alumina, magnesia, and mixtures thereof are preferred supports. The iron-based catalysts are prepared by methods which include precipitation, coprecipitation, impregnation, vapor deposition, and the formation of metal complexes (i.e., metal carbonyl, etc.) and the like. The impregnation of a porous inorganic oxide support, such as alumina, with a solution of an iron salt and an alkali or alkaline-earth metal component, via cocurrent or sequential impregnation, with subsequent drying, calcination and reduction of the supported iron catalyst by contact and treatment of the catalyst with hydrogen or hydrogen and ammonia, or ammonia in admixture with another reducing gas, or gases, has been found to provide a highly active catalyst for the hydrodenitrogenation of nitrogen-containing compounds. Impregnation of the support with iron, or iron and other metal promoters or modifiers, by the incipient wetness technique, or technique wherein the iron nd other metal promoters or modifiers are contained in solution in measured amount and an entire solution absorbed into the support, subsequently dried, calcined, and activated by contact with hydrogen, or hydrogen and ammonia, or ammonia in admixture with another reducing gas has been found particularly satisfactory in preparing a supported catalyst. The supported iron catalyst is promoted or modified with alkali or alkaline-earth metals, or metal oxides such as sodium, potassium, cesium, magnesium, calcium, barium, or the like. The alkali or alkaline-earth metal, or metals, or compounds thereof are added to the catalyst in concentrations ranging from about 0.01 percent to about 10 percent, preferably from about 0.2 percent to about 4 percent, based on the total weight of metal, exclusive of the weight of the support. Sodium, potassium, cesium, magnesium, calcium, and barium are the preferred alkali or alkaline-earth metals. Aluminum, or compound thereof, suitably an oxide, is also as already noted a preferred promoter, or modifier, and it is preferably employed in or contained within the catalyst in concentration ranging from about 0.01 percent to about 20 percent, preferably from about 0.5 percent to about 5 percent, calculated as aluminum oxide (Al.sub.2 O.sub.3), based on the total weight of the supported component, exclusive of the weight of the support. Rhenium, nickel, cobalt, palladium, platinum, and copper metals, or compounds thereof, can also be added to the catalyst as promoters or modifiers, these metals generally being added to the catalyst in concentrations ranging from about 0.01 percent to about 10 percent, preferably in concentration ranging from about 0.5 percent to about 2.5 percent, based on the weight of the supported component, exclusive of the weight of the support. After impregnation of the support, the metal impregnated support is dried generally at temperatures ranging from about 65.degree. C. to about 280.degree. C., preferably from about 80.degree. C. to about 110.degree. C., in circulating air, vacuum or microwave oven. The calcination is suitably conducted at temperatures ranging from about 300.degree. C. to about 650.degree. C., preferably from about 450.degree. C. to about 550.degree. C.
The iron catalysts can be reduced, and activated by contact with hydrogen, by sequential contact with hydrogen and ammonia, or reduced and activated by contact with an admixture of ammonia and hydrogen or by contact with an admixture of ammonia and another reducing gas or gases. The reducing gas and ammonia can be generated in situ or ex situ. The catalysts are more effectively activated if contacted with a stream of flowing hydrogen, or a stream characterized as an admixture of hydrogen and ammonia, or admixture of ammonia and another reducing gas, or gases. Nitrogen-containing compounds which under pretreat conditions can thermally or reductively decompose to generate ammonia, can also be added to a reducing gas, e.g., hydrogen, and the gaseous mixture contacted with the iron catalysts for the activation thereof. In addition, other pretreatment conditions may be used in combination with reduction in order to modify and/or enhance the catalyst. Treatment with a hydrogen rich blend with some carbon containing gas, e.g., carbon monoxide or carbon dioxide, can be used to introduce carbon to the catalyst.
The catalyst is reactivated, after deactivation, by contact with hydrogen, or by contact with ammonia in admixture with hydrogen, or ammonia in admixture with another reducing gas, or gases. Similarly, the activity-maintenance of the catalyst can sometimes be improved during an operating run by introducing ammonia, or ammonia in admixture with another gas, or gases, with the nitrogen-containing feed. In general, the ammonia is employed in admixture with another gas, or gases, in concentration ranging from about 0.01 percent to about 20 percent, preferably from about 0.2 percent to about 10 percent, based on the volume of the gas.
The the catalyst is activated, pretreated, or reactivated by contact with the reducing gas, or gaseous admixture, at temperatures ranging from about 300.degree. C. to about 600.degree. C., preferably from about 400.degree. C. to about 500.degree. C. Suitable pressures range from about 0 psig to about 2000 psig, preferably from about 0 psig to about 1200 psig. Hydrogen partial pressures generally range from about 0 psig to about 2000 psig, preferably from about 0 psig to about 1200 psig, and more preferably from about 0 psig to about 600 psig. Space velocities generally range from about 100 GHSV to about 10,000 GHSV, preferably from about 1000 GHSV to about 5000 GHSV.
Pure or mixed feeds can be processed in accordance with this invention to hydrodenitrogenate nitrogen-containing compounds. These can include pure aliphatic amines, e.g., primary amines such as methylamine, N-ethylhydroxyamine, n-butylamine, sec-butylamine, n-octylamine, and the like; secondary amines such as diethylamine, dipropylamine, diiso-butylamine, N,N-diethylhydroxyamine, and the like, and tertiary amines such as trimethylamine, trioctylamine and the like; aromatic amines, e.g., aniline, m-toluidine, benzylamine, o-phenylenediamine, 1-naphthylamine, diphenylamine, 3,4-biphenyldiamine, and the like; nitrogen-containing heterocyclic compounds such as 2-aminopyrrole, 1-aminoacridine, and the like. In hydrode-nitrogenating the pure aliphatic compounds the amino group is cleaved; and if there is unsaturation in the molecule, the molecule is generally saturated with hydrogen. In hydrodenitrogenating nitrogen-containing compounds such as quinoline it is found that the nitrogen-containing ring is first hydrogenated, and the carbon-nitrogen bond then cleaved to produce ring opening of the portion of the molecule which contains the nitrogen atom. Thereafter the second carbon-nitrogen bond is cleaved and nitrogen removed without hydrogen saturation of the remaining aromatic ring. Similarly so with such compounds as carbazole and acridine; the nitrogen-containing ring is saturated with hydrogen, the carbon-nitrogen bond is then cleaved, the carbon sites from whereon the nitrogen atom was previously attached are healed with hydrogen, and the nitrogen atom then hydrogenated to form ammonia. In neither instance is there any significant hydrogen saturation of the non-nitrogen containing aromatic rings. The invention finds its greatest utility however, in the treatment of nitrogen-containing feedstocks such as encountered in a refinery environment. Thus, naphthas, middle distillates, inclusive of diesel fuels, jet fuels, various solvents, light gas oil, heavy gas oils and vacuum bottoms and residuals all contain nitrogen in varying concentrations, whether derived from conventional petroleum feeds or non-conventional feedstocks such as tar sands, coal liquids, shale oils, and the like.